A. There appears to be an increase in the incidence of adenocarcinoma subtype of NSCLC in the USA. In particular, tumors with features characteristic of bronchiole-alveolar carcinomas appear to be increasing. The relatively large number of cell lines that we have established that have ultrastructural and biochemical evidence of arising from peripheral airway cells (Clara or Type II pneumocyte) confirms these findings. Markers for differentiation in lung cancers include expression of Clara and surfactant genes (in adenocarcinomas) and N-cam in neuroendocrine tumors. In addition, expression of CEA is much higher in neuroendocrine lung cancers than in others. B. SCLC cell lines retain their chemosensitivity patterns for many years, and in vitro testing is predictive of patient response and survival. Thus, panels of cell lines (SCLC, NSCLC, colorectal and gastric carcinomas) are useful reagents to screen putative new phase I and II drugs using the MTT tetrazolium dye assay. E. Mutations of ras genes are a characteristic of a subset of NSCLC, but are not found in SCLC.